config.mk: Remove unused HPATH

This variable is not unused anywhere.

Signed-off-by: Shinya Kuribayashi <skuribay@pobox.com>

config.mk

@@ -196,7 +196,7 @@ endif
 
 #########################################################################
 
-export	HPATH HOSTCC HOSTCFLAGS CROSS_COMPILE \
+export	HOSTCC HOSTCFLAGS CROSS_COMPILE \
 	AS LD CC CPP AR NM STRIP OBJCOPY OBJDUMP MAKE
 export	TEXT_BASE PLATFORM_CPPFLAGS PLATFORM_RELFLAGS CPPFLAGS CFLAGS AFLAGS